The 38-year-old actor, whose seven-year-old son, Ayaan, was diagnosed with first-stage cancer in 2014, took to Twitter to make the announcement.
"Work on a documentary on cancer has begun. It's in its initial stages. It's important to create awareness about 'the C word'," wrote Hashmi.
Last year, the "Azhar" actor co-authored a book with Bilal Siddiqui, titled "The Kiss of Life: How A Superhero and My Son Defeated Cancer", wherein apart from his life and career anecdotes, he shared his and his family's struggles in dealing with his son's diagnosis.